nbd: make the config put is called before the notifying the waiter

[ Upstream commit 87aac3a80af5cbad93e63250e8a1e19095ba0d30 ]

There has one race case for ceph's rbd-nbd tool. When do mapping
it may fail with EBUSY from ioctl(nbd, NBD_DO_IT), but actually
the nbd device has already unmaped.

It dues to if just after the wake_up(), the recv_work() is scheduled
out and defers calling the nbd_config_put(), though the map process
has exited the "nbd->recv_task" is not cleared.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index edf8b632e3d27b4b907a52dd55e41e3a6b8a03ef..f46e26c9d9b3c19d34bfda53c186d2e50c4564d7 100644 (file)
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -801,9 +801,9 @@ static void recv_work(struct work_struct *work)
                if (likely(!blk_should_fake_timeout(rq->q)))
                        blk_mq_complete_request(rq);
        }
+       nbd_config_put(nbd);
        atomic_dec(&config->recv_threads);
        wake_up(&config->recv_wq);
-       nbd_config_put(nbd);
        kfree(args);
 }